This invention relates generally to epitaxial growth techniques, and more particularly to growth of Group II-VI semiconductor crystalline materials.
As is known in the art, Group II-VI semiconductor epitaxial materials such as cadmium telluride and mercury cadmium telluride have important applications as photodetector elements for detection of electromagnetic energy in the special range from approximately 0.8 .mu.m to 30 .mu.m. By adjusting an alloy composition of cadmium and mercury, photodetector elements are provided which are sensitive to different wavelength ranges within the 0.8 .mu.m to 30 .mu.m wavelength band.
Several different techniques have been suggested for providing cadmium telluride and mercury cadmium telluride suitable for use in photodetector applications. One method suggested is metalorganic vapor phase expitaxy (MOVPE), also referred to metalorganic chemical vapor deposition (MOCVD). As it is known, the MOCVD technique for growing mercury cadmium telluride involves directing vapors of mercury, dimethylcadmium, and diethyltelluride into a reactor vessel and chemically reacting the directed vapors to provide the epitaxial material.
Several problems are encountered in the art of growing mercury cadmium telluride epitaxial layers by the MOCVD technique. One problem of particular importance is the compositional uniformity of the deposited epitaxial layers provided by the MOCVD technique.
Generally, the composition of these layers varies from the downstream portion of the substrate to the upstream portion. This compositional variation generally involves a progressively increasing depletion of Cd towards the downstream or back portion of the substrate whereas the upstream portion or front portion of the substrate is generally excessively rich in Cd. Variations in the lateral and side to side compositional uniformity Cd are generally also present.
The prevalent view regarding the chemical reaction mechanisms which occur in Group II-VI materials grown by MOCVD is set forth in an article entitled "Organometallic Growth of II-VI Compounds" by J. B. Mullin et al, Journal of Crystal Growth, Volume 55, 1981, pp. 92-106. In this article, the authors suggest that the directed alkyls of tellurium and cadmium may not pyrolyse independently. Rather, the authors suggest that adducts or complexes of these compounds are produced because DMCd (dimethylcadmium) and DETe (diethyltelluride) are attracted to one another in the vapor phase forming a weak bond. In the authors' view, the decomposition of these adducts leads to the formation of the Group II-VI materials and other products.